While there is continuing a demand for a finer pattern rule in the drive for higher integration and operating speeds in LSI devices, active efforts have been devoted to develop the microfabrication technology utilizing deep- and vacuum-ultraviolet lithography.
In particular, the ArF excimer laser is widely acknowledged as a light source of next generation to the KrF excimer laser and indispensable for the photolithography of 90-45 nm node advanced semiconductor devices. While polyhydroxystyrene derivatives played a main role as the base resin in resist compositions of the KrF excimer laser generation, they are difficultly applicable to the photolithography using the ArF excimer laser as the light source because they are opaque to wavelength 193 nm. For the ArF excimer laser photolithography, it is the key factor to search for base resins having transparency.
Poly(meth)acrylic acid and derivatives thereof were considered attractive as the resins which are fully transparent at 193 nm and have relatively satisfactory development properties, but left a problem of dry etching resistance. For improving dry etching resistance, poly(meth)acrylate derivatives having alicyclic structures such as adamantane and norbornane structures incorporated in the pendant ester moiety were developed as described in JP-A 4-39665 and JP-A 5-257281. They become the main stream of development work.
These derivatives, however, are still insufficient in etching resistance. It is expected from the future pattern miniaturization trend that etching resistance will become a factor of more significance because formation of a thinner film of resist is essential to acquire a resolution.
Also proposed in the art are resins having an alicyclic structure as the backbone, for example, polynorbornene derivatives and alternating copolymers of polynorbornene derivatives and maleic anhydride. Although some have sufficient etching resistance, there remains unsolved the problem of poor resolution due to inferior development properties, i.e., swelling and low dissolution contrast during development.
Also, for reducing the load to the mask design, improving only the maximum resolution is insufficient, and the proximity bias (or pattern density difference) must be reduced concomitantly.